Ganged potentiometer construction



May 29, 1956 M. BURGESS 2,748,230

GANGED POTENTIOMETER CONSTRUCTION Filed Sept. 25, 1953 3 Sheets-Sheet 1 May 29, 1956 M. BURGESS 2,748,230

GANGED POTENTIOMETER CONSTRUCTION Filed Sept. 25, 1953 3 Sheets-Sheet 2 May E39, 1956 L. M. BURGESS 2,74%,239

GANGED POTENTIOMETER CONSTRUCTION 3 Sheets-Sheet 3 Filed Sept. 23, 1953 Mil/l! mmuunnmw m ill GANGED POTENTIOMETER CONSTRUCTION Lauren M. Burgess, Lexington, Mass, assignor, by mesne assignments, to Acton Laboratories, Inc, Boston, Mass.

Application September 23, 1953, Serial No. 381,900

Claims. (Cl. 201--55) The present invention relates to ganged variable resistor constructions, and more particularly to a ganged potentiometer construction wherein the individual potentiometers may be removed easily and quickly and new ones substituted therefore.

In certain control mechanisms large numbers of ganged variable resistors or potentiometers are employed. Each of the potentiometers or variable resistors is connected to a particular circuit, and the various potentiometers may have ditferent resistance values and characteristics. The potentiometers are driven in unison due to their ganged relation, but sometimes it is desired to quickly replace one of the potentiometers either due to the necessity of changing the characteristics desired, or merely replacing a potentiometer which no longer seems to exhibit its original characteristics. Accordingly it would be desirable to provide an improved ganged potentiometer construction to facilitate changing the individual components quickly and readily.

It, therefore, is an object of the present invention to provide a ganged variable resistor construction where in the individual resistor units may be adjusted readily relative to each other, and quickly assembled and disassembled.

Still another object of the invention is to provide in a ganged potentiometer construction an arrangement whereby the individual potentiometers will be plugged into electrical socket connectors for quick assembly and disassembly.

Still another object of the invention is to provide in variable resistors or potentiometers an improved interconnecting means between the shafts of the individual units without the use of tools or adjusting devices.

A still further object of the invention is to provide an inter-connection between the units between the driving and driven arms so that they are in close proximity to the contact arm engaging the variable resistor, thereby to assure the best possible operation and proper alignment.

Still another object of the invention is to provide in a variable resistor an arrangement for inter-connecting a plurality of resistor units so that the inter-connection has rigidity in a plane perpendicular to the shaft and has compliance perpendicular to that plane.

A still further object of the invention is to provide inter-locking casings for the potentiometers to exclude foreign matter and to provide for simple retention of the cases in interlocked relation by a single locking band or ring.

Still another object of the invention is to provide in a plug-in ganged assembly of variable resistors or potentiometers provision for a limited amount of phase adjustment between the individual potentiometer units.

Still another object of the invention is to provide in a potentiometer low driving torque, and minimum backlash.

A still further object of the invention is to provide in a potentiometer an improved contact assembly having Patented May 29, 1956 Too optimum operation under conditions of vibration, shock and high speed.

A still further object of the invention is to provide in a potentiometer an assembly having a low leakage path for the contact assembly.

Other and further objects of the invention subsequently will become apparent by reference to the following description taken in conjunction with the accompanying drawings, wherein:

Figure 1 is a side view with portions thereof broken away to show parts thereof in longitudinal cross-section in two planes A and B;

Figure 2 is a vertical cross-section view as seen in the direction of the arrows along the line 2--2 of Figure 1;

Figure 3 is a view as seen in the direction of the arrows along the line 3-3 of Figure 1; and showing the locations of the planes A and B referred to in connection with Figure 1;

Figure 4 is a cross-sectional view showing a detail of the inter-connecting members;

Figure 5 is a perspective view of the contact arm and slip ring connections;

Figure 6 is a view as seen in the direction of the arrows along the line 6-6 of Figure 1, and also showing the location of the planes referred to in connection with Figure 1;

Figure 7 is a side view of the support element;

Figure 8 is a perspective view of the locking band or ring;

Figure 9 is a perspective view of the inter-connecting driven arm;

Figure 10 is a cross-sectional view showing details of the inter-locking casings; and

Figure 11 is a detailed view of a portion of Figure 1 showing the bearing assembly and loading.

Referring to Figure 1 there is illustrated an assembly or plurality of variable resistors or potentiometers connected together so that the wiper arms of the various potentiometers are driven in unison. This assembly includes a front mounting member having a supporting bracket 11 carrying a supporting member 12 of circular configuration having a peripheral edge to engage the inter-locking edge portions of a potentiometer or variable resistor. The suporting member 12 may be secured to the support 11 by a cap screw or screws 13. The support member 12 has a central opening 14 of sufficient size to provide adequate clearance for a drive shaft 15, which is adapted to be connected by a set screw 16 to the shaft of a potentiometer.

The assembly has a rear support bracket 17, which carries a support member 18 of circular configuration having a periphery which will conform to the inter-locking peripheral edge of a variable resistor or potentiometer. The support member 18 may carry a stub shaft 19 for cooperation with the shaft of the last potentiometer or variable resistor, although the shaft 19 is not essen tial for many installations. The support 18 in Figure 1 is shown engagement with a housing 21 of a conventional potentiometer or variable resistor 22 having a shaft 23 and a driving and wiper arm 24. The conventional potentiometer 22 is fitted in inter-locking relation to the adjacent potentiometer, and is retained in position by a clamp ring 25 which preferably is of the type shown in United States Letters Patent 2,543,673.

It is proposed in accordance with the present invention to arrange in ganged relation a plurality of variable resistors or potentiometers, and to make provision for quickly connecting and disconnecting such potentiometers by means of a socket and plug connection. For this purpose there has been provided for each variable resistor or potentiometer a support structure comprising a base 26 provided with a plurality of contact prongs 27 mounted within an auxiliary base structure 28 secured to the bottom of the base 26. Extending vertically from the sides of the base 26 are a pair of finger grips 29 so that the prongs 27 may be withdrawn from the cooperating socket or connector. The upper surface of the base 26 has an arcuate concave surface so as to be complementary to the outer curved surface of the casing of a potentiometer. The base 26 also carries a locking band or ring 31 held in position by a pair of screws 32 passing into suitable threaded apertures in the base 26.

For a better understanding of further details of the contemplated invention, reference will best be had to Figures 1, 2 and 6. From this it will be noted that the base 26 is provided with a plurality of threaded apertures 33 for receiving the fastening screws 26 for the locking band 29. It further will be noted that preferably the vertical finger grip members 29 are made of molded material having internal recesses 34 to accommodate electrical conductors 35 which inter-connect the prongs 27 with connector contacts 36 carried by an insulating block .37 on a potentiometer housing or casing 38. Also it will be noted that the sub-base member 28 preferably is secured to the base 26 by a plurality of cap screws 39.

Certain details of the variable resistors or potentiometers carried by the base 26 are shown in Figures 1, 2, 3 and 6. In Figure l the upper half of the potentiometer adjacent the front support is shown as seen in the direction of the arrows along the plane passing through the center and identified by the letter A36. The lower half of the potentiometer shown in Figure 1 is a cross-sectional view as seen in the direction of the arrows along the plane B passing through the center of the potentiometer shaft as indicated by Figures 3 and 6. This has been done in order to show the relation of the parts with the greatest clarity. The potentiometer casing 38 carries on its inner cylindrical surface a sheet of insulating fiber or material 41 which is engaged by a resistor element 42. Such resistor element most commonly consists of a fiber insulating card upon which has been wound turns of resistance wire. For simplicity in the present disclosure, however, the resistance element 42 has been shown to be of the type where the resistance material has been deposited on a suitable supporting surface. The particular type of resistance element forms no critical part of the present invention. The ends of the resistance element 42 are connected to suitable electrical terminals or binding posts 36. Where desired, the insulating member 37 may carry additional binding posts or contacts 36, which in turn may be connected to tapped points on the resistance element 42 and also to a slip ring 43 carried by an insulating sleeve 44 mounted on a boss 45 in the front wall 46 of the potentiometer housing or casing 38. The boss 45 has a central opening in which are positioned ball bearing members 47 and a shaft 48. The shaft 48 at its forward end is either engaged by a driving member such as the stub shaft 15, or another member subsequently to be described. The rear end of the shaft 48 is connected to a bell crank 49 of insulation having two arms 51 and 52. The bell crank arm 51 of insulation provides a low leakage path for a unitary assembly carried thereby and shown in detail in Figure 5. This assembly 53 has two depending bifurcated arms 54, each formed of suitable precious metal having bent contact portions 55 for engaging the slip ring 43. The two bifurcated precious metal arms are connected to a vertical member 56 having a suitable aperture 57 for receiving a cap screw or rivet 58 which engages a suitable aperture in the bell crank arm 51. The vertical member 56 is bent over to form a generally horizontal member 59 having an extending lug 61. The extending lug 61 is spot welded to a reversely bent bifurcated precious metal contact arm 62 having bent contact portions 63 for engaging the resistance element 42.

The use of precious metal bifurcated arms 54 for engaging the slip ring 43 has shown a reduction in the amount of torque required and an appreciable reduction in the electrical noise of the device. These contact portions have a high natural resonant frequency, and by having two contact portions there is less likelihood of an interruption of the circuit under certain conditions of operation, such as high speed or vibration. The bifurcated precious metal contact arm 62. also produces a reduction in the electrical noise of the device, and there are fewer possibilities of electrical discontinuity due to the two portions of the arm 62 engaging the resistance element 42. Here again the precious metal contact arm 62 had a high natural resonant frequency so that the arms will be quick in following any rapid motion of the shaft 48.

From Figures 3 and 6 it will be noted that the contact portions 63 of the arm member 62 are in close proximity to the bell crank arm 52. The bell crank arm 52 carries a stud 6 t'or coupling together a bell crank arm 52 which constitutes a driving arm and a driven arm which is mounted on the next succeeding potentiometer or variable resistor. The next succeeding variable resistor carries a driven arm assembly 65 shown in detail in Figure 9. This comprises a clamping portion 66 having an extending lug 67, to which is welded a relatively thin extension member 63 having an aperture 69. The aperture 69 is formed with two angularly arranged lug portions 71 for engaging the sides of the pin 64. The assembly 65 is so designed that in the plane perpendicular to the shaft of a potentiometer the assembly is rigid, while in a plane perpendicular to that plane the member 68 has a certain amount of compliance. This assures convenient alignment of successive potentiometer assemblies even though certain manufacturing tolerances are present. The manner in which the pin 64 of the arm 52 engages the aperture in the extension member 68 of the assembly 67 is shown in detail in Figure 4. It will be noted that the end of the pin 64 is engaged by the cooperating angularly arranged member 71.

It has been found that the use of ball bearing members 47 for the shaft 48 and the resilient driven arm assembly 65 has greatly minimized the backlash and torque characteristics as contrasted to former characteristics so as to produce a 10 to 1 overall improvement. The improvement in backlash has been obtained by this cooperation and the fact that the bell crank arm 52 engages the stud 64 with but a small angle between the pin 64 and the contact portions 63 of the arm 62 for engaging the resistance element 42.

Figure 10 shows certain constructional details of the casings of the variable resistors or potentiometers and the locking band or ring 31. It will be noted that potentiometer case 38A near its rear end has an anular groove 72 and that the case 3313 has a similar annular groove 73. The locking band or ring 31 engages both grooves 72 and 73 to hold the case together. It will be noted that the ring 31 is generally concave so as to engage the inclined edges of the annular recesses 72 and 73 so that tightening the ring tends to draw the two cases closer together.

It further will be noted that the end of the case 38A has an annular reduced diameter portion 74, while the front of the case 38B has an inner annular recess 75 to accomodate the reduced diameter portion 74 of the adjacent potentiometer case 33A. This stepped interlock connection precludes the possibility of foreign matter entering into the cases when they are arranged as shown in Figure 1.

The clamping ring 31 not only serves to hold together the inter-locking edges of adjacent potentiometers or variable resistors, but also provides a means whereby limited angular phase adjustment may be made. It, of course, will be appreciated that in mounting the various resistors 42 within the respective potentiometer casings that there might be some variation in the position thereof with respect to the outer portion of the casing or the terminal block 37. The inter-connection between the shafts of the two potentiometers generally is such so there should be an alignment of the various contact points 63 on the wiper arm's of the various potentiometers. However, any variation in their position with respect to each other or the resistor elements 42 with respect to each other can be corrected quickly and simply by rotation of the casing or housing 38 by the desired amount, whereupon the clamping ring 31 is then tightened to retain the casing in proper adjusted phase relation.

From the foregoing it will be appreciated that the arrangement disclosed offers certain advantages in ease of assembly, in adjustment of the parts relative to each other, and in the convenient replacement of any component. Among the other advantages in the arrangement shown is the simplified unitary construction of the element of Figure 5 comprising the wiper arm contact 36 and the two slip ring brush contacts 55. Any need for replacement of this member is accomplished conveniently by removal of the cap screw 58. It further will be noted that as seen in Figure l a rather compact ganged assembly is obtainable by means of the base 26. The single locking band or ring 31 serves to hold the components in proper alignment with respect to each other, and provides for phase adjustment When needed.

Figure 11 shows in enlarged detail the shaft 48 mounted in bearings 37. Two similar bearings 47 are employed and preloaded by the use of bearing shields 20. Each bearing shield is formed with three different portions, the larger central portion 30 having on each side reduced diameter annular portions 40 and 50. These two portions are somewhat smaller in diameter than the inner diameter of the outer race member of the ball bearing assembly 47. In order to minimize the radial play of the shaft 48, the bearings 47 are pre-loaded by the shields 20, which also serve to keep dirt and foreign particles from entering the bearing races and bearings 47. Pre-loading is accomplished by mounting the left hand shield 20 so as to take up the space between the inner race member of the bearing 47 and the arm 52, and the left hand bearing shield 20 is applied to the other bearing 47. The driving member 15 is pressed against the shield 20 while pressure is being applied to the right hand of the shaft 48, and then the member 15 is tightened. The bearing shields 20, therefore, tend to move inwardly toward each other the inner race members of the ball bearing assembly 47. The bearing shield portion 30 is so positioned that not more than .005 clearance is obtained between that member and the outer race member of the bearing 47. This .005 clearance is eifectively sealed by grease when the device is assembled. In the case of the next succeeding potentiometer the same assembly procedure employed by the driving member 65 is used to pre-load the bearings in the same manner as the driving member 15 was used in the case of the left hand potentiometer.

While for the purpose of illustrating and describing the present invention certain preferred embodiments have been illustrated in the drawings, it is to be understood that the invention is not to be limited thereby since such variations and other embodiments are contemplated as may be commensurate with the spirit and scope of the invention set forth in the accompanying claims.

I claim as my invenion:

1. A support assembly for potentiometers having terminals on top arranged in a horizontal gang for a single control comprising a base having a plurality of electrical contact prongs for engaging a connector socket, a pair of finger grips extending upwardly from said base, said grips having a reduced inner surface to receive electrical conductors inter-connecting said prongs with the terminals of a potentiometer, said base having an arcuate recess for receiving the cylindrical case of a potentiometer, an arcuate locking band in a plane parallel to the plane of said finger grips, said band having openings at each end, and screw means passing through said openings into said base.

2. A support assembly for potentiometers having terminals on top arranged in a gang for a single control comprising a base for each potentiometer, said base having a plurality of electric contact prongs for engaging a connector socket, a pair of finger grips extending upward ly from said base and partially surrounding said potentiometer, said grips having a reduced inner surface to receive electrical conductors inter-connecting said prongs with the terminals of a potentiometer, said base having an arcuate recess for receiving the cylindrical case of a potentiometer, an arcuate locking band in a plane parallel to the plane of said finger grips, said band having openings at each end, said band being adapted to engage the edge of a potentiometer case carried by said base and the edge of an adjacent potentiometer case, screw means passing through said openings into said base.

3. A ganged variable resistor assembly comprising a plurality of variable resistors each having a cylindrical casing provided with a peripheral recess adjacent the front and rear ends, said casing having an annular configuration at its front end to fit in inter-locking manner with the rear end of an adjacent casing, a shaft carrying an insulated bell crank having a unitary wiper contact and slip ring contact, each shaft at the front end carrying a driven arm to be engaged by one arm of said bell crank, a plurality of supports for said resistors each comprising a base having a plurality of electric contacts, said base having a concave upper surface complementary to the cylindrical resistor casing, a plurality of electric conductors for inter-connecting said contacts with the variable resistor, and a concave arcuate locking band having its end secured to said base, said band engaging an annular recess of the variable resistor casing supported on the base and a recess of an adjacent resistor.

4. In a variable resistor having a cylindrical casing, a resistor element and a rotatable shaft carrying at its forward end a driven lever arm, the combination comprising a unitary bell crank, one arm of said crank carrying a contact for engaging the resistor element in the vicinity of the other arm of said crank, said other arm having means for engaging the driven lever arm of an adjacent variable resistor.

5. In a variable resistor having a cylindrical casing, a resistor element and a rotatable shaft carrying at its forward end a resilient apertured driven lever arm, the combination comprising a unitary bell crank, one arm of said crank carrying a contact for engaging the resistor element in the vicinity of the other arm of said crank, said other arm having a pin for engaging the aperture of the driven lever arm of an adjacent variable resistor.

6. In a variable resistor having a cylindrical casing carrying a resistor element, a slip ring and a rotatable shaft, the combination comprising a driven lever mounted on the front end of said shaft, said lever having rigidity in a plane perpendicular to the shaft and compliance perpendicular to said plane, a bell crank mounted at the other end of said shaft, one arm of said crank carrying a member to be engaged by the driven lever of an adjacent resistor, the other arm of said crank carrying the unitary electric contact structure having two legs for engaging a slip ring, and a third reversely folded leg making contact with said resistor element in the proximity of the first arm of said bell crank.

7. In a variable resistor having a cylindrical casing carrying a resistor element, a slip ring and a rotatable shaft, the combination comprising a driven lever mounted on the front end of said shaft, said lever having rigidity in a plane perpendicular to the shaft and compliance perpendicular to said plane, a bell crank mounted on the other end of said shaft, one arm of said crank carrying a pin to be engaged by the driven lever of an adjacent resistor, the other arm of said crank carrying a unitary electric contact structure having two legs for engaging opposite sides of a slip ring, and a third reversely folded leg having adjacent its outer end a contact for engaging said resistor element in the proximity of the first arm of said bell crank.

8. In a potentiometer having a cylindrical slip ring and a shaft carrying an insulated arm, a unitary contact assembly carried by said arm comprising two leg portions for engaging said slip ring and a third reversely bent leg for making contact with the resistor element of the potentiometer, said latter leg being bifurcated to terminate in two bent portions for simultaneous contact with the resistor element, said bifurcated leg having a high natural resonant frequency.

9. In a potentiometer having a cylindrical slip ring and a shaft carrying an insulated arm, a unitary contact assembly carried by said arm having two leg portions of precious metal for engaging said slip ring and a third leg of precious metal for making contact with the resistor element of the potentiometer, each of said leg portions being bifurcated to terminate in contact portions, each leg portion having a high natural resonant frequency.

10. In a precision variable resistor, the combination comprising a cylindrical housing having an axial opening, a pair of ball bearings mounted at each end of said opening each having an outer race engaging said opening to preclude further inward movement thereof, a shaft carried by the inner races of said bearings, an arm secured to one end of said shaft, a bearing seal interposed between said arm and the adjacent bearing, said seal having an annular portion arranged to engage the inner race of the bearing, a bearing seal positioned on said shaft ad jacent the other bearing, said seal having an annular portion arranged to engage the inner race of said latter hearing, a driving member mounted on the other end of said shaft in engagement with said latter seal whereby the inner races of said ball bearings are preloaded toward each other.

References Cited in the file of this patent UNITED STATES PATENTS 2,592,392 Canziani Apr. 8, 1952 2,593,332 Mucher Apr. 15, 1952 2,675,451 Tinus Apr. 13, 1954 FOREIGN PATENTS 537,121 Germany Oct. 15, 1931 

